[EXT] Re: [PATCH v3] vhost: compilation fix for GCC-12

[Amit Prakash Shukla]

Hi Maxime,

Sure, I will test and reply on your patch.

Thanks,
Amit Shukla

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin at redhat.com>
> Sent: Thursday, October 6, 2022 12:55 PM
> To: Amit Prakash Shukla <amitprakashs at marvell.com>; Chenbo Xia
> <chenbo.xia at intel.com>
> Cc: dev at dpdk.org; Jerin Jacob Kollanukkaran <jerinj at marvell.com>;
> stable at dpdk.org; Ruifeng.Wang at arm.com
> Subject: [EXT] Re: [PATCH v3] vhost: compilation fix for GCC-12
> 
> External Email
> 
> ----------------------------------------------------------------------
> Hi Amit,
> 
> On 10/6/22 09:22, Amit Prakash Shukla wrote:
> > Ping.
> 
> I posted a patch yesterday that fixes this issue without having to change the
> runtime behavior:
> 
> https://urldefense.proofpoint.com/v2/url?u=http-
> 3A__patches.dpdk.org_project_dpdk_patch_20221005203524.89336-2D1-
> 2Dmaxime.coquelin-
> 40redhat.com_&d=DwICaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=ALGdXl3fZgFG
> R69VnJLdSnADun7zLaXG1p5Rs7pXihE&m=vDZyV-
> pKSmtssm0L8YUPR6doPgIw44tOh3xWgNEwD3FGjqEomaP9lcYLhrbqwGKb&s
> =g54ujCkU-mDT0CQoJgqYlDllGLuzWs8lLa6YMzPfqkw&e=
> 
> Could you test it and provide ack if OK on your side?
> 
> Thanks,
> Maxime
> 
> >> -----Original Message-----
> >> From: Amit Prakash Shukla <amitprakashs at marvell.com>
> >> Sent: Friday, September 2, 2022 8:36 PM
> >> To: Maxime Coquelin <maxime.coquelin at redhat.com>; Chenbo Xia
> >> <chenbo.xia at intel.com>
> >> Cc: dev at dpdk.org; Jerin Jacob Kollanukkaran <jerinj at marvell.com>;
> >> stable at dpdk.org; Ruifeng.Wang at arm.com; Amit Prakash Shukla
> >> <amitprakashs at marvell.com>
> >> Subject: [PATCH v3] vhost: compilation fix for GCC-12
> >>
> >> GCC-12 complains about the possible use of un-initialized array. At
> >> compile time it seems like it is not able to evaluate the size as it
> >> involves run-time variable and at compile time it seems like gcc
> >> assumes value of "size" variable to be zero which makes gcc-12 to jump
> the while loop.
> >> "size = pkt->pkt_len + sizeof(struct virtio_net_hdr_mrg_rxbuf);"
> >>
> >> As part of the fix, "while (){}" is replaced by "do {} while()" which
> >> make the compiler to generate a code in which buf_vec will never be
> >> used un- initialized.
> >>
> >> ../lib/vhost/virtio_net.c:941:35: error:
> >> 		'buf_vec[0].buf_len' may be used uninitialized
> >> 		[-Werror=maybe-uninitialized]
> >>    941 |         buf_len = buf_vec[vec_idx].buf_len;
> >>        |                   ~~~~~~~~~~~~~~~~^~~~~~~~
> >> ../lib/vhost/virtio_net.c: In function 'virtio_dev_rx_packed':
> >> ../lib/vhost/virtio_net.c:1285:27: note: 'buf_vec' declared here
> >>   1285 |         struct buf_vector buf_vec[BUF_VECTOR_MAX];
> >>        |                           ^~~~~~~
> >> cc1: all warnings being treated as errors
> >>
> >> Fixes: 93520085efda ("vhost: add packed ring single enqueue")
> >> Cc: stable at dpdk.org
> >>
> >> Signed-off-by: Amit Prakash Shukla <amitprakashs at marvell.com>
> >> ---
> >> v2:
> >> - Changes for code review suggestion
> >>
> >> v3:
> >> - Added a description
> >>
> >>   lib/vhost/virtio_net.c | 8 ++++----
> >>   1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c index
> >> b3d954aab4..9b77d3d10f 100644
> >> --- a/lib/vhost/virtio_net.c
> >> +++ b/lib/vhost/virtio_net.c
> >> @@ -1069,7 +1069,7 @@ vhost_enqueue_single_packed(struct virtio_net
> >> *dev,
> >>   	else
> >>   		max_tries = 1;
> >>
> >> -	while (size > 0) {
> >> +	do {
> >>   		/*
> >>   		 * if we tried all available ring items, and still
> >>   		 * can't get enough buf, it means something abnormal @@ -
> >> 1097,7 +1097,7 @@ vhost_enqueue_single_packed(struct virtio_net
> *dev,
> >>   		avail_idx += desc_count;
> >>   		if (avail_idx >= vq->size)
> >>   			avail_idx -= vq->size;
> >> -	}
> >> +	} while (size > 0);
> >>
> >>   	if (mbuf_to_desc(dev, vq, pkt, buf_vec, nr_vec, num_buffers,
> >> false) < 0)
> >>   		return -1;
> >> @@ -1574,7 +1574,7 @@ vhost_enqueue_async_packed(struct virtio_net
> >> *dev,
> >>   	else
> >>   		max_tries = 1;
> >>
> >> -	while (size > 0) {
> >> +	do {
> >>   		/*
> >>   		 * if we tried all available ring items, and still
> >>   		 * can't get enough buf, it means something abnormal @@ -
> >> 1601,7 +1601,7 @@ vhost_enqueue_async_packed(struct virtio_net
> *dev,
> >>   		avail_idx += desc_count;
> >>   		if (avail_idx >= vq->size)
> >>   			avail_idx -= vq->size;
> >> -	}
> >> +	} while (size > 0);
> >>
> >>   	if (unlikely(mbuf_to_desc(dev, vq, pkt, buf_vec, nr_vec,
> >> *nr_buffers, true) < 0))
> >>   		return -1;
> >> --
> >> 2.25.1
> >